1. Field of the Invention
The present invention relates to a vibrating or linear compressor which can be used for a refrigerator.
2. Related Art
A vibrating compressor is used for a refrigerator because of a simple configuration, compact and light weight features, a high force rate, and low power consumption. There is a conventional vibrating compressor described in Japanese Patent Publication No. 5-23347 of 1993 as one of the conventional vibrating compressors. The conventional vibrating compressor is described below with reference to FIG. 24.
Referring to FIG. 24, there are shown a control circuit 1, a temperature detecting section 1-1, a calculating section 1-2, a driving circuit 1-3, temperature detectors 2 and 3, a driving section 4, a compressor 5, a condenser 6, a vacuum device 7, a refrigerator 8, and an evaporator 8-1. The control circuit 1, which comprises a temperature detecting section 1-1, a calculating section 1-2, and a driving circuit 1-3, outputs a driving signal of a frequency driven by the compressor 5 based on a signal from the temperature detector 2 for detecting a temperature corresponding to a saturated vapor pressure of refrigerant taken in by the compressor 5 and the temperature detector 3 for detecting a temperature corresponding to a saturated vapor pressure of refrigerant which is ejected with compression by the compressor 5.
Now an operation of the conventional vibrating compressor is described below. The temperature detecting section 1-1 converts a signal detected by the temperature detectors 2 and 3 to a predetermined electric signal. The calculating section 1-2 generates a voltage corresponding to a frequency driven by the compressor 5 based on "a temperature corresponding to an intake pressure" and "a temperature corresponding to an ejecting pressure" converted to an electric signal by the temperature detectors 2 and 3. The driving circuit 1-3 is used to supply a driving signal of a frequency corresponding to a voltage supplied by the calculating section to the driving section 4 and the driving section 4 is used to drive the compressor 5 with a driving force corresponding to the driving signal.
However, there is a problem in a vibrating compressor made by using conventional techniques that a compression efficiency is lowered due to unstable strokes of a piston caused by changes of a driving force supplied to the compressor by the driving section since there is an error between a true refrigerant temperature representing a refrigerant pressure and a temperature detected by the temperature detector and an input voltage to the driving section changes due to changes of a power voltage, and in some cases, a valve of a cylinder is damaged by a strike of the piston against the valve.
In case of a configuration that an upper dead point reference position of the piston is previously set to a position far from a valve to prevent the valve from being damaged by a strike of the piston, there is a problem that a compression efficiency is further lowered since refrigerant cannot be compressed sufficiently. In addition, there is a problem that a refrigeration capability is reduced due to changes of strokes of the piston caused by changes of a spring coefficient of a mechanical system formed by refrigerant gas and a resonance spring because of changes of an external air temperature, a power voltage, and a load.
Furthermore, there is a problem that an efficiency is further lowered due to a difference between a resonance frequency of the mechanical system formed by the refrigerant gas and the resonance spring and a resonance frequency of an electric system for driving the mechanical system since there is an error between a true refrigerant temperature representing a refrigerant pressure and a temperature detected by a temperature detector.
As another type of a conventional vibrating compressor, there is, for example, a vibrating compressor described in Japanese Utility Model Laid-open No. 2-145679 of 1990. The conventional vibrating compressor will be described referring to FIG. 25.
In FIG. 25, there are shown an alternating power source 41, a variable voltage rectifier 42, a pressure instruction generator 43, a summing amplifier 44, a frequency oscillator 45, a pulse signal generator 46, a orthogonal converter 47, a linear motor 48, a compressor 49, a pressure tank 50, a vibrating compressor 51, and a pressure detector 52.
The alternating power source 41 is used to supply power to the variable voltage rectifier 42 and the variable voltage rectifier 42 is used to supply power to the orthogonal converter 47 on the basis of the power applied by the alternating power supply 41 and a signal given by the pulse signal generator 46. An operation of this type of the conventional vibrating compressor is described below. The pressure instruction generator 43 is used to give a pressure instruction to the summing amplifier 44 and the summing amplifier 44 is used to add a pressure instruction given by the pressure instruction generator 43 to a pressure value detected by the pressure detector 52 to be amplified and to output a signal to the frequency oscillator 45. The frequency oscillator 45 oscillates a frequency based on a signal given by the summing amplifier 44, and the pulse signal generator 46 gives a pulse signal to the orthogonal converter 47 based on a frequency oscillated by the frequency oscillator 45. The orthogonal converter 47 drives the linear motor 48 constituting the vibrating compressor 51 by using power supplied by the variable voltage rectifier 42 based on a signal generated by the pulse signal generator 46.
The compressor 49 takes in refrigerant, compresses it, and ejects it in the pressure tank 50 when the linear motor 48 is driven. The pressure detector 52 detects a pressure of refrigerant ejected from the pressure tank 50 and outputs a signal to the summing amplifier 44. Use of the conventional vibrating compressor is intended to operate the vibrating compressor 51 as expected by controlling frequency oscillated by the frequency oscillator 45 even if there is a difference between a pressure instructed by the pressure instruction generator and a pressure of the pressure tank 50 detected by the pressure detector 52.
The vibrating compressor, however, has a problem that a compression efficiency is reduced due to a difference between an actual operating frequency and a resonance frequency since it cannot detect a change of the resonance frequency of the vibrating compressor caused by a change of load conditions. In addition, there is a problem that a frequency control itself is likely to be uncertain or unstable since there is an error between a true refrigerant pressure and a pressure detected by the pressure detector and a time lag occurs in a detected pressure according to a position at which the pressure detector is installed.